Asbestos and Disease

Introduction:

Asbestos is a fibrous mineral, of which there are various types.
The fibres are very narrow and are therefore easily respirable. Their resistance
to chemical dissolution means that they will persist for a long time -
perhaps indefinitely once they have settled in the lung.

Hazards and Risks

A survey conducted by the Health and Safety Executive indicated that
in the UK the highest risk of asbestos related lung disease arises from
insulation work. In one group studied more than 10% of men died of mesothelioma.
Epidemiologic work by Professor Peto has shown that in the first couple of
decades of the 21st century we can continue to expect a rise in the number of new
cases of mesothelioma in Great Britain. mesotheliome is a horrible cancer
of the lining of the lung (usually), with a very long latency period
(it can manifest itself 40 years after asbestos exposure or even longer).

Although it is difficult to estimate exposure-response relationships
for mesothelioma, it may be somewhat easier to do so for asbestosis (a
progressive fibrotic disease of the lungs caused by relatively heavy exposure
to asbestos):

....."our best judgement as to the lifetime occupational exposure to
asbestos at which the fibrotic process cannot advance to .... Asbestosis
is in the range of 25 f/cc-yrs and below" (Ontario Royal Commission,
1984)

Risk from exposure within buildings:

There have been various attempts to estimate the risk from exposure within
buildings and summaries of two of these are given below:-

D.O.E. (U.K.)

usually < 0.0005 f ml-1 (> background, regulated fibres).

40 hrs/week for 20 years = attributable
Life-time risk of death of ~ 1 = 100,000.+

Ontario Royal Commission

assume 0.001 f ml-1 ,

work exposure for 10 years = attributable risk of death risk 20:1,000,000.*

* about 1/50 of death risk of 10mile drive/working
day for same time

+about 1/100 of death risk
for non-smokers from passive exposure to smoke ( ~ 1/10 cigarette/day)

Therefore, provided the asbestos is well contained in structural
elements such as tiles or cement, well sealed and left undisturbed (no
drilling, sawing, or unscrupulous demolition), the risk of asbestos related
disease should be negligibly small - arguably smaller than the risk of
removing it.

Asbestosis, Mesothelioma and other asbestos-related lung disease

Broadly speaking asbestos can cause two types of damage
in humans: Cancer e.g. mesothelioma; and fibrous
thickening (either within the alveolar structure of the lung, or in its
pleural lining)

Asbestosis is often classified separately from pneumoconiosis even though
asbestos is a dust - but it is a special form of fibrous dust. Like silicosis,
asbestosis is a serious condition which is incurable and can result in
death at an early age. However, as is the case with many harmful substances
it does require a certain inhaled dose of asbestos before there is a measurable
risk of asbestosis. Thus, living or working in a building in which asbestos
has been used in construction and suitably sealed will not result in a
high enough inhaled dose and thus cannot cause asbestosis.

The accompanying image shows asbestos bodies in human bronchoalveolar
fluid obtained through bronchoalveolar lavage (BAL) by the author for diagnostic
and research purposes from a symptomatic worker who had significant exposure
to asbestos (note alveolar macrophage cells adherent to the larger body,
close to a large multinucleated giant cell, while in the bottom right hand
corner a smaller body has probably been engulfed by a couple of the cells).

This photomicrograph shows an asbestos body under higher
magnification, surrounded by alveolar macrophages (the phagocytic cells
resident in the alveoli). Asbestos bodies are not simply asbestos fibres
but are characterised by a covering containing iron and protein (ferritin).
These photomicrographs clearly show how difficult it is for a macrophage to
engulf and ingest asbestos fibres. This leads to a "frustrated
macrophage" situation which is believed to explain, at least in part, the
toxicity of such fibres.Note also the small dark inclusions in many of the macrophages - these
are probably the consequence of tobacco smoking.

Asbestosis is often classified separately from pneumoconiosis even though
asbestos is a dust -but it is a special form of fibrous dust. Like silicosis,
asbestosis is a serious condition which is incurable and can result in
death at an early age. However, as is the case with many harmful substances
it does require a certain inhaled dose of asbestos before there is a measurable
risk of asbestosis. Thus, living or working in a building in which asbestos
has been used in construction and suitably sealed will not result in a
high enough inhaled dose and thus cannot cause asbestosis.

(Note: the term "asbestosis" is only used for
one specific disease caused by asbestos and not for all its health effects.
Other effects can include thickening and/or calcification of the pleura.
Asbestos can also cause a special cancer of the pleura called mesothelioma
as well as bronchial cancer similar to that caused by smoking.)

Sadly, not all information or instruction is
useful and appropriate. Information alone is not a substitute for reasonable
risk reduction strategies. Consider the accompanying photograph for example.
The photo was taken by the author in the 1980s. You would be very surprised
to find out where: In a National Health Service Hospital in England!

Would you consider that advising workers not to inhale blue asbestos
is a reasonable way of protecting their health, and preventing ill-health?

With an attitude such as the one exemplified by the above photo is not
surprising that sadly people will continue to die of mesothelioma for decades
to come as a legacy of the terrible indifference in the past.

Bronchial cancer

("lung" cancer)

The single most important known environmental respiratory carcinogen
by far in man is tobacco smoke. However lung cancer may also be caused
by other agents notably. asbestos, (but also certain compounds of nickel,
polycyclic aromatic hydrocarbons (PAH) e.g. benzpyrene, arsenic trioxide
and chromates).

Relative risk of Lung cancer+

There are about 45,000 deaths from lung (bronchial) cancer
per year in U.K. - 90% of them are caused by tobacco
smoking. If a person is a smoker as well as having been exposed to
asbestos, then in absolute terms the risk of developing lung (bronchial
cancer) is greater than the simple addition of the risks from tobacco or
smoking alone.

Mesothelioma

Exposure to asbestos dusts probably of all kinds but especially of blue
asbestos (crocidolite) can cause mesothelioma which is a cancer of the
pleural lining of the lung or much less commonly of the peritoneum.This
disease is essentially incurable, and commonly leads to a great deal
of pain and other suffering. (This incidence of mesothelioma is besides
an increased risk of lung cancer in the bronchus as with smokers, and which
has been discussed above). Thousands of ex-workers still die of these diseases
in the UK every year.

Information about the reported incidence of asbestos
related disease in the UK is collected by the SWORD
scheme, and to a lesser extent by other schemes which are also part of the THOR
network at the University
of Manchester.

Prevention:

Asbestos has now been banned for most purposes in most developed
countries. Substitutes such as the various types of MMMF (man made mineral
fibre) are generally much less hazardous although not completely free from
risk. Sophisticated risk assessment and riosk management steps must be
in place prior to any asbestos demolition or clearance.